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| Dissertation / PhD Thesis/Book | PreJuSER-5064 |
2009
Forschungszentrum Jülch GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-89336-577-7
Please use a persistent id in citations: http://hdl.handle.net/2128/3687
Abstract: This thesis focusses on the influence of interlayer coupling on the magnetization dynamics of heterostructure systems. This topic has been investigated by time-resolved photoemission electron microscopy (PEEM) using a pump-probe approach. Magnetic and chemical contrast is provided by the llumination with circularly polarized x-rays due to the x-ray magnetic circular dichroism (XMCD) effect. In this way the spatially resolved magnetodynamic response of the single layers in asymmetric trilayer samples on short magnetic field pulses was studied. The measurements have been carried out at the electron storage rings ESRF (Grenoble) and BESSY-II (Berlin). Samples with different material combinations have been deposited by molecular beam evaporation (MBE) and magnetron sputtering and subsequently micro-structured by optical lithography and Argon ion beam milling. Combining PEEM and magnetooptical Kerr effect (MOKE) studies the coupling conditions have been investigated. In CoFe/Cr/ NiFe and Fe/Cr/Co systems oscillatory interlayer exchange coupling depending on the Cr spacer thickness was found, while the Heusler-based Co$_{2}$MnSi/MgOCo$_{2}$FeSi system showed a roughness-induced orange-peel coupling. Time-resolved measurements have been carried out on single films and interlayer exchange coupled trilayers. In single-crystalline iron films the influence of the agnetocrystalline anisotropy on the magnetodynamic response was studied. A bulging of the domain walls was found experimentally and in micromagnetic simulations. This effect is discussed in terms of an inhomogeneous demagnetizing field within the magnetic elements. In heterostructures the competition between single film properties such as shape and magnetocrystalline anisotropy and the interlayer exchange coupling was studied. The single films showed an inhomogeneous response with a locally varying coupling strength due to locally enhanced magnetic stray fields at domain walls or defects. The results are discussed in terms of the local energy contributions. By varying the temporal shape of the excitation field different magnetodynamic reactions have been investigated. Using short magnetic field pulses magnetic eigenmodes have been excited that have been reproduced by macro-spin calculations. The frequency of the eigenmode was found to be considerably increased due to the interlayer coupling.
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